Generally, the present invention is related to vehicles having an internal combustion engine and a rotary electric machine operatively coupled through a gear set to an output shaft. The output shaft in turn is operatively coupled to a final drive through a multi-ratio transmission. Such arrangements are known having various operating modes through which torque transfers between and among the engine, the electric machine, and the output shaft are controllable to effectuate desired operational objectives.
It has been recognized that certain preferred compound planetary gear set arrangements hold promising potential for such diverse operating modes, among them being vehicle drive modes wherein positive torque is produced at the drive wheels to propel the vehicle. Such drive modes may be characterized by a positive engine torque and a positive electric machine torque wherein the electric machine contributes motoring or inertial torque, or by a positive engine torque and a negative electric machine torque wherein the electric machine diverts a generating torque. The present invention is directed toward a vehicle drive mode of the latter variety specifically during vehicle launch wherein the vehicle is accelerated from a substantially static condition.